fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-PYPDF-13658705
- https://snyk.io/vuln/SNYK-PYTHON-PYPDF-13658706

Author: snyk-bot

requirements.txt

@@ -1,6 +1,6 @@
 fpdf2==2.7.6
 pathspec==0.11.2
-pypdf==3.17.0
+pypdf==6.1.3
 Pygments==2.15.1
 pyinstaller==5.13.1
 pytest==7.3.1